Wireless communication method and wireless communication terminal in high density environment including overlapped basic service sets

ABSTRACT

Provided is a wireless communication terminal that communicates wirelessly. The wireless communication terminal includes: a transceiver; and a processor. The processor receives a first PLCP Protocol Data Unit (PPPU) through the transceiver, and transmits a second PPDU based on Basic Service Set (BSS) information indicated by the first PPDU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/942,764 filed on Jul. 30, 2020, which is a continuation of U.S.patent application Ser. No. 15/968,681 filed on May 1, 2018, issued asU.S. Pat. No. 10,764,924 dated Sep. 1, 2020, which is a continuation ofInternational Patent Application No. PCT/KR2016/012615 filed on Nov. 3,2016, which claims the priority to Korean Patent Application No.10-2015-0154100 filed in the Korean Intellectual Property Office on Nov.3, 2015, Korean Patent Application No. 10-2015-0156467 filed in theKorean Intellectual Property Office on Nov. 9, 2015, Korean PatentApplication No. 10-2016-0062425 filed in the Korean IntellectualProperty Office on May 20, 2016, Korean Patent Application No.10-2016-0074091 filed in the Korean Intellectual Property Office on Jun.14, 2016 and Korean Patent Application No. 10-2016-0086044 filed in theKorean Intellectual Property Office on Jul. 7, 2016, the entire contentsof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication method and awireless communication terminal in a high-density environment includingan overlapped basic service set.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelesscommunication technology that can provide a rapid wireless Internetservice to the mobile apparatuses has been significantly spotlighted.The wireless communication technology allows mobile apparatusesincluding a smart phone, a smart pad, a laptop computer, a portablemultimedia player, an embedded apparatus, and the like to wirelesslyaccess the Internet in home or a company or a specific service providingarea.

One of most famous wireless communication technology is wireless LANtechnology. Institute of Electrical and Electronics Engineers (IEEE)802.11 has commercialized or developed various technological standardssince an initial wireless LAN technology is supported using frequenciesof 2.4 GHz. First, the IEEE 802.11b supports a communication speed of amaximum of 11 Mbps while using frequencies of a 2.4 GHz band. IEEE802.11a which is commercialized after the IEEE 802.11b uses frequenciesof not the 2.4 GHz band but a 5 GHz band to reduce an influence byinterference as compared with the frequencies of the 2.4 GHz band whichare significantly congested and improves the communication speed up to amaximum of 54 Mbps by using an Orthogonal Frequency DivisionMultiplexing (OFDM) technology. However, the IEEE 802.11a has adisadvantage in that a communication distance is shorter than the IEEE802.11b. In addition, IEEE 802.11g uses the frequencies of the 2.4 GHzband similarly to the IEEE 802.11b to implement the communication speedof a maximum of 54 Mbps and satisfies backward compatibility tosignificantly come into the spotlight and further, is superior to theIEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless communicationtechnology standards after the 802.11ac and 802.11ad, discussion forproviding a high-efficiency and high-performance wireless communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless communication technology environment,communication having high frequency efficiency needs to be providedindoors/outdoors under the presence of high-density terminals and baseterminals and various technologies for implementing the communicationare required.

Especially, as the number of devices using a wireless communicationtechnology increases, it is necessary to efficiently use a predeterminedchannel Therefore, required is a technology capable of efficiently usingbandwidths by simultaneously transmitting data between a plurality ofterminals and base terminals.

DISCLOSURE Technical Problem

An object of the present invention is to provide a wirelesscommunication method and a wireless communication terminal in ahigh-density environment including an overlapped basic service set.

Technical Solution

According to an embodiment of the present invention, a wirelesscommunication terminal that communicates wirelessly includes: atransceiver; and a processor, wherein the processor is configured toreceive a first PLCP Protocol Data Unit (PPPU) through the transceiver,and transmit a second PPDU based on Basic Service Set (BSS) informationindicated by the first PPDU.

When a BSS indicated by the first PPDU is different from a BSS includingthe wireless communication terminal and the first PPDU includes atrigger frame, the processor may be configured to measure an receivedsignal strength of the first PPDU, and when the second PPDU istransmitted after transmission of the first PPDU is completed, theprocessor may be configured to adjust a transmission power of the secondPPDU based on the received signal strength.

The processor may be configured to receive a third PPDU that is anuplink PPDU transmitted based on the trigger frame through thetransceiver, and after decoding a signaling field of the third PPDU, theprocessor may be configured to transmit the second PPDU based on thesignaling field of the third PPDU.

The wireless processor may be configured to decode the signaling fieldof the third PPDU to determine whether the third PPDU is transmittedbased on the first PPDU, and adjust the transmission power of the secondPPDU based on whether the third PPDU is transmitted based on the firstPPDU.

The processor may be configured to determine whether the third PPDU istransmitted based on the first PPDU based on whether a BSS colorindicated by the signaling field of the third PPDU is equal to a BSScolor of the BSS including the wireless communication terminal.

The processor may be configured to set a value of a network allocationvector (NAV) according to the BSS indicated by the third PPDU.

The signaling field of the third PPDU may be configured to include aparameter determined based on a magnitude of interference acceptable bya wireless communication terminal transmitting the first PPDU whenreceiving the third PPDU and a transmission power of the first PPDU,wherein the processor may be configured to adjust the transmission powerof the second PPDU based on a value of the parameter and the receivedsignal strength.

The value of the parameter may be a value normalized over a 20 MHzfrequency band width.

When the BSS indicated by the first PPDU is different from the BSSincluding the wireless communication terminal, the processor may beconfigured to perform CCA by applying an overlapped BSS (OBSS) CCAthreshold value that is greater than a CCA threshold value applied to aPPDU transmitted from the BSS including the wireless communicationterminal, and adjust a transmission power of the second PPDU inconjunction with the OBSS CCA threshold value.

When transmitting a fourth PPDU within a transmission opportunity (TXOP)obtained when transmitting the second PPDU, the processor may beconfigured to adjust a transmission power of the fourth PPDU inconjunction with the OBSS CCA threshold value.

The signaling field of the second PPDU may be configured to include afield indicating that the transmission power is adjusted.

According to an embodiment of the present invention, an operation methodof a wireless communication terminal that communicates wirelesslyincludes: receiving a first PLCP Protocol Data Unit (PPPU) through thetransmission/reception unit, and transmitting a second PPDU based onBasic Service Set (BSS) information indicated by the first PPDU.

The transmitting of the second PPDU may include: when a BSS indicated bythe first PPDU is different from a BSS including the wirelesscommunication terminal and the first PPDU includes a trigger frame,measuring an received signal strength of the first PPDU; and when thesecond PPDU is transmitted after transmission of the first PPDU iscompleted, adjusting a transmission power of the second PPDU based onthe received signal strength.

The transmitting of the second PPDU may include: receiving a third PPDUthat is an uplink PPDU transmitted based on the trigger frame throughthe transmission/reception unit, and after decoding a signaling field ofthe third PPDU, transmitting the second PPDU based on the signalingfield of the third PPDU.

The transmitting of the second PPDU based on the signaling field of thethird PPDU after the decoding of the signaling field of the third PPDUmay include: decoding the signaling field of the third PPDU to determinewhether the third PPDU is transmitted based on the first PPDU; andadjusting the transmission power of the second PPDU based on whether thethird PPDU is transmitted based on the first PPDU.

The decoding of the signaling field of the third PPDU to determinewhether the third PPDU is transmitted based on the first PPDU mayinclude determining whether the third PPDU is transmitted based on thefirst PPDU based on whether a BSS color indicated by the signaling fieldof the third PPDU is equal to a BSS color of the BSS including thewireless communication terminal.

The transmitting of the second PPDU may further include setting a valueof a network allocation vector (NAV) according to the BSS indicated bythe third PPDU.

The signaling field of the third PPDU may include a parameter determinedbased on a magnitude of interference acceptable by a wirelesscommunication terminal transmitting the first PPDU when receiving thethird PPDU and a transmission power of the first PPDU, wherein theadjusting of the transmission power of the second PPDU may includeadjusting the transmission power of the second PPDU based on a value ofthe parameter and the received signal strength.

The transmitting of the second PPDU may include: performing CCA byapplying an overlapped BSS (OBSS) CCA threshold value that is greaterthan a CCA threshold value applied to a PPDU transmitted from the BSSincluding the wireless communication terminal, and adjusting atransmission power of the second PPDU in conjunction with the OBSS CCAthreshold value.

The operating method may further include when transmitting a fourth PPDUwithin a transmission opportunity (TXOP) obtained when transmitting thesecond PPDU, adjusting a transmission power of the fourth PPDU inconjunction with the OBSS CCA threshold value.

Advantageous Effects

An embodiment of the present invention is to provide a wirelesscommunication method and a wireless communication terminal in a denseenvironment including an overlapped basic service set.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless LAN system according to an embodiment of thepresent invention.

FIG. 2 shows a wireless LAN system according to another embodiment ofthe present invention.

FIG. 3 shows a block diagram illustrating a configuration of a stationaccording to an embodiment of the inventive concept.

FIG. 4 shows a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 shows a process that a station sets an access point and a linkaccording to an embodiment of the present invention.

FIG. 6 shows a case where a BSS including a wireless communicationterminal according to an embodiment of the present invention isoverlapped with another BSS.

FIG. 7 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation during anuplink multiplex transmission of an OBSS.

FIG. 8 shows that when a trigger frame is transmitted through thenon-legacy PPDU format from OBSS, a wireless communication terminalaccording to an embodiment of the present invention performs an SRoperation during an uplink multiplex transmission based on a triggerframe.

FIG. 9 shows that when a trigger frame is transmitted through the legacyPPDU format from OBSS, a wireless communication terminal according to anembodiment of the present invention performs an SR operation during anuplink multiplex transmission based on a trigger frame.

FIG. 10 shows that when a non-legacy PPDU including a trigger frame anda data frame together is transmitted in OBSS, a wireless communicationterminal according to an embodiment of the present invention performs anSR operation during an uplink multiplex transmission based on a triggerframe.

FIG. 11 shows that when a trigger-based UL MU PPDU is transmitted fromOBSS, a wireless communication terminal according to an embodiment ofthe present invention sets a NAV.

FIG. 12 shows an operation of a wireless communication terminalaccording to an embodiment of the present invention to increase thedegree of spatial reuse when a UL MU PPDU is transmitted from OBSS.

FIG. 13 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

FIG. 14 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

FIG. 15 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a legacy PPDUincluding a trigger frame is transmitted from the OBSS.

FIG. 16 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation based on acontention procedure when a PPDU including a trigger frame istransmitted from the OBSS.

FIG. 17 shows an operation of a wireless communication terminal to set aNAV according to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

FIG. 18 shows an operation of a wireless communication terminal to set aNAV according to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

FIG. 19 shows that a wireless communication terminal according to anembodiment of the present invention transmits a PPDU by adjustingtransmission power in an SR operation.

FIG. 20 shows that when a UL MU PPDU is transmitted from an OBSS, awireless communication terminal according to an embodiment of thepresent invention performs an SR operation while protecting an ACK framefor an UL MU PPDU transmitted from the OBSS.

FIG. 21 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Parts notrelating to description are omitted in the drawings in order to clearlydescribe the present invention and like reference numerals refer to likeelements throughout.

Furthermore, when it is described that one comprises (or includes orhas) some elements, it should be understood that it may comprise (orinclude or has) only those elements, or it may comprise (or include orhave) other elements as well as those elements if there is no specificlimitation.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2015-0154100 (2015 Nov. 3), Nos. 10-2015-0156467(2015 Nov. 9), Nos. 10-2016-0062425 (2016 May 20), Nos. 10-2016-0074091(2016 Jun. 14), and Nos. 10-2016-0086044 (2016 Jul. 7) filed in theKorean Intellectual Property Office and the embodiments and mentioneditems described in the respective applications are included in theDetailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless communication systemaccording to an embodiment of the present invention. For convenience ofdescription, an embodiment of the present invention is described throughthe wireless LAN system. The wireless LAN system includes one or morebasic service sets (BSS) and the BSS represents a set of apparatuseswhich are successfully synchronized with each other to communicate witheach other. In general, the BSS may be classified into an infrastructureBSS and an independent BSS (IBSS) and FIG. 1 illustrates theinfrastructure BSS between them.

As illustrated in FIG. 1 , the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a concept including a wireless LAN communication devicesuch as non-AP STA, or an AP, or both terms. A station for wirelesscommunication includes a processor and a transceiver and according tothe embodiment, may further include a user interface unit and a displayunit. The processor may generate a frame to be transmitted through awireless network or process a frame received through the wirelessnetwork and besides, perform various processing for controlling thestation. In addition, the transceiver is functionally connected with theprocessor and transmits and receives frames through the wireless networkfor the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless communicationsystem according to another embodiment of the present invention. Forconvenience of description, another embodiment of the present inventionis described through the wireless LAN system. In the embodiment of FIG.2 , duplicative description of parts, which are the same as orcorrespond to the embodiment of FIG. 1 , will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3 , the station 100 according to the embodimentof the present invention may include a processor 110, a transceiver 120,a user interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN physical layer frame, or the like and may be embeddedin the station 100 or provided as an exterior. According to theembodiment, the transceiver 120 may include at least one transmit andreceive module using different frequency bands. For example, thetransceiver 120 may include transmit and receive modules havingdifferent frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. Accordingto an embodiment, the station 100 may include a transmit and receivemodule using a frequency band of 6 GHz or more and a transmit andreceive module using a frequency band of 6 GHz or less. The respectivetransmit and receive modules may perform wireless communication with theAP or an external station according to a wireless LAN standard of afrequency band supported by the corresponding transmit and receivemodule. The transceiver 120 may operate only one transmit and receivemodule at a time or simultaneously operate multiple transmit and receivemodules together according to the performance and requirements of thestation 100. When the station 100 includes a plurality of transmit andreceive modules, each transmit and receive module may be implemented byindependent elements or a plurality of modules may be integrated intoone chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 may be a modulator and/or demodulator whichmodulates wireless signal transmitted to the transceiver 120 anddemodulates wireless signal received from the transceiver 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4 , the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4 , among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4 , the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3 , thetransceiver 220 of the AP 200 may also include a plurality of transmitand receive modules using different frequency bands. That is, the AP 200according to the embodiment of the present invention may include two ormore transmit and receive modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a transmit and receive module using a frequency band of 6 GHz ormore and a transmit and receive module using a frequency band of 6 GHzor less. The respective transmit and receive modules may performwireless communication with the station according to a wireless LANstandard of a frequency band supported by the corresponding transmit andreceive module. The transceiver 220 may operate only one transmit andreceive module at a time or simultaneously operate multiple transmit andreceive modules together according to the performance and requirementsof the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 may be a modulatorand/or demodulator which modulates wireless signal transmitted to thetransceiver 220 and demodulates wireless signal received from thetransceiver 220. The processor 210 controls various operations such asradio signal transmission/reception of the AP 200 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5 , the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5 , the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

Due to the spread of mobile devices and the supply of wirelesscommunication, wireless communication terminals are increasinglycommunicating in a dense environment. Particularly, the number of caseswhere a wireless communication terminal communicates in an environmentin which a plurality of BSSs are overlapped is increasing. When multipleBSSs are overlapped, the communication efficiency of the wirelesscommunication terminal may be degraded due to interference with otherwireless communication terminals. In particular, when a frequency bandis used through a contention procedure, a wireless communicationterminal may not obtain even a transmission opportunity due tointerference with other wireless communication terminals. To solve thisproblem, a wireless communication terminal may perform a spatial reuse(SR) operation. Specifically, the SR operation may include an operationof accessing the channel depending on whether the received frame is aframe transmitted from a BSS including a wireless communication terminalor a frame transmitted from another BSS. In a specific embodiment, theoperation of accessing the channel may include a CCA operation and adeferral operation. For example, the wireless communication terminal mayadjust a Clear Channel Assessment (CCA) threshold according to whether aframe received by the wireless communication terminal is a frametransmitted from a BSS including the wireless communication terminal ora frame transmitted from an OBSS. Also, the wireless communicationterminal may adjust the transmission power of the PPDU to be transmittedin the SR operation. An embodiment for an SR operation of the wirelesscommunication terminal will be described with reference to FIGS. 6 to 21.

For convenience of explanation, a BSS including a wireless communicationterminal is referred to as Intra-BSS, and a basic service set overlappedwith Intra-BSS is referred to as an Overlapped Basic Service Set (OBSS).In addition, a frame transmitted in the Intra-BSS is referred to as anIntra-BSS frame, and a frame transmitted in the OBSS is referred to asan OBSS frame or an Inter-BSS frame.

FIG. 6 shows a case where a BSS including a wireless communicationterminal according to an embodiment of the present invention isoverlapped with another BSS.

In the embodiment of FIG. 6 , the first BSS BSS1 includes station A STAA and station B STA B. In addition, the second BSS BSS2 includes stationC STA C and station D STA D. When the station C STA C transmits a PPDUto the station D STA D, the magnitude of an interference to the stationB STA B may be smaller than the magnitude of an interference to thestation A STA A. This is because both the stations A and B are includedin the second BSS corresponding to the OBSS of the first BSS BSS1 butthe distances from the station C are different. Therefore, based on therelative position of the OBSS receiving wireless communication terminalreceiving the frame transmitted from the OBSS, the wirelesscommunication terminal may estimate the magnitude of a potentialinterference that the transmission of the wireless communicationterminal affects the reception of the OBSS receiving wirelesscommunication terminal. At this time, the wireless communicationterminal may estimate the potential interference based on the receivedsignal strength (RSSI) of the PPDU transmitted by the OBSS receivingwireless communication terminal. Accordingly, the wireless communicationterminal may estimate the potential interference based on the receivedsignal strength (RSSI) of the PPDU transmitted by the OBSS receivingwireless communication terminal.

A data frame is transmitted by a transmission sequence including aplurality of transmissions. For example, the wireless communicationterminal may transmit a data frame and receive an ACK/Block ACK frame.In addition, the wireless communication terminal may transmit a requestto send (RTS) frame, receive a clear to send (CTS) frame, transmit adata frame, and receive an ACK frame. Therefore, the wirelesscommunication terminal may estimate the interference that thetransmission of the wireless communication terminal affects thereception of the response frame for the corresponding frame based on thereceived signal strength of any one frame in the transmission sequence.

The wireless communication terminal may transmit the PPDU based on theestimated potential interference. Specifically, the wirelesscommunication terminal may increase the degree of spatial reuse. In aspecific embodiment, the wireless communication terminal may adjust thetransmission power of the PPDU to be transmitted in the SR operation.For example, when a wireless communication terminal receives a PPDU froma wireless communication terminal located a relatively long distancefrom the wireless communication terminal, the wireless communicationterminal may transmit the PPDU with a transmission power larger than thetransmission power used when the PPDU is received from the wirelesscommunication terminal located at a relatively short distance. At thistime, whether the wireless communication terminal is located at arelatively long distance may be determined based on the received signalstrength value of the PPDU transmitted by the corresponding wirelesscommunication terminal. In the embodiment of FIG. 6 , when the station ASTA A receives the PPDU to be transmitted to the station B STA B, thestation C STA C may measure the received signal strength RSSI AC of thecorresponding PPDU. When the station B STA B transmits a PPDU to thestation A STA A, the station C STA C may determine the transmissionpower based on the measured received signal strength RSSI AC andtransmit the PPDU to the station D STA D with the determinedtransmission power. In addition, the station C STA C may measure thereceived signal strength RSSI BC of the corresponding PPDU when thestation B STA B transmits it to the station A STA A. At this time, whenthe RSSI AC is larger than the RSSI BC, when the station A STA Areceives a PPDU from the station B STA B, the station C STA C maytransmit the PPDU with a transmission power lower than the transmissionpower used when the station B STA B receives the PPDU from the station ASTA A.

Also, the wireless communication terminal may change the CCA thresholdvalue during the SR operation. Specifically, when a wirelesscommunication terminal located at a relatively long distance from awireless communication terminal receives the PPDU, the wirelesscommunication terminal may use a clear channel assessment (CCA)threshold value that is larger than a CCA threshold value used when awireless communication terminal located at a relatively short distancereceives a PPDU. In this case, the CCA threshold value may be areference value for determining whether the channel is idle. In theembodiment of FIG. 6 , the station C STA C may measure the receivedsignal strength RSSI AC of the PPDU that the station A STA A transmitsto the station B STA B. When the station B STA B transmits a PPDU to thestation A STA A, the station C STA C may determine the CCA thresholdvalue based on the measured received signal strength RSSI AC andtransmit the PPDU to the station D STA D based on the determined CCAthreshold value. In addition, the station C STA C may measure thereceived signal strength RSSI BC of the PPDU that the station B STA Btransmits to the station A STA A. At this time, when the RSSI AC islarger than the RSSI BC, when the station A STA A receives a PPDU fromthe station B STA B, the station C STA C may transmit the PPDU based ona CCA threshold value greater than a CCA threshold value used when thestation B STA B receives the PPDU from the station A STA A.

In addition, the operation of increasing the degree of spatial reuse mayinclude an operation of changing the CCA threshold value to a referencevalue when the CCA threshold value is smaller than the reference value.In addition, the operation of increasing the degree of spatial reuse mayinclude an operation of resetting or reconfiguring an existing value ofa network allocation vector (NAV) by a wireless communication terminal.At this time, the NAV is an indicator indicating that the wirelessmedium (WM) is busy for transmission between the other wirelesscommunication terminals. When NAV is set in the wireless communicationterminal, the wireless communication terminal may not be able to accessthe corresponding channel regardless of the CCA result. In addition, theoperation of increasing the degree of spatial reuse may include anoperation in which the wireless communication terminal transmits thePPDU irrespective of the CCA result. Specifically, the wirelesscommunication terminal may perform CCA using an infinite CCA thresholdvalue, and determine that the corresponding channel is always idle. Inaddition, the operation of increasing the degree of spatial reuse mayinclude an operation in which the wireless communication terminal resetsor reconfigures the NAV, and then transmits the PPDU based on the CCAusing energy sensing.

In the above-described embodiments, the wireless communication terminalmay increase the degree of spatial reuse based on the received signalstrength of the PPDU transmitted by the OBBS receiving wirelesscommunication terminal for a predetermined time period. At this time,the predetermined time period may be a time period during which the OBSSreceiving wireless communication terminal receives the response PPDU forthe PPDU transmitted by the OBSS receiving wireless communicationterminal. In addition, a certain time period may indicate the number ofdesignated frames. This is because the channel condition may be changedover time, and the wireless communication terminals included in the OBSSmay move.

FIG. 7 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation during anuplink multiplex transmission of an OBSS.

As described above, a general transmission sequence is initiated by awireless communication terminal having a frame to be transmitted.Further, in order to consider reception of a frame transmitted from theOBSS, the wireless communication terminal must consider the relativeposition of the OBSS receiving wireless communication terminal or thedistance between the wireless communication terminal and the OBSSreceiving wireless communication terminal. At this time, the OBSSreceiving wireless communication terminal indicates a wirelesscommunication terminal receiving a frame transmitted from the OBSS.Further, the wireless communication terminal may determine the relativeposition of the OBSS receiving wireless communication terminal or thedistance between the wireless communication terminal and the OBSSreceiving wireless communication terminal based on the PPDU transmittedby the OBSS receiving wireless communication terminal. Accordingly, thewireless communication terminal must receive at least two PPDUs from theinitiation of the transmission sequence to determine the relativeposition of the OBSS receiving wireless communication terminal or thedistance between the wireless communication terminal and the OBSSreceiving wireless communication terminal. Accordingly, it is possibleto perform an operation of increasing the degree of spatial reuse(degree of spatial reuse) by receiving at least two PPDUs from theinitiation of the transmission sequence.

However, in case of uplink (UL) multi-user (MU) transmission, an accesspoint to receive a data frame may initiate a transmission sequence bytransmitting a trigger frame. Specifically, a plurality of wirelesscommunication terminals may receive a trigger frame from an access pointand transmit the UL MU PPDU to the access point based on the triggerframe. Accordingly, the wireless communication terminal may initiate theoperation of increasing the degree of spatial reuse from the middle oftransmission of the PPDU transmitted based on the trigger frame.Specifically, the wireless communication terminal may initiate theoperation of increasing the degree of spatial reuse after decoding thesignaling field of the PPDU transmitted based on the trigger frame. Thewireless communication terminal may determine whether the correspondingPPDU is the UL MU PPDU transmitted based on the trigger frame throughthe signaling field of the PPDU. In addition, the wireless communicationterminal may increase the degree of spatial reuse based on the receivedsignal strength of the PPDU including the trigger frame transmitted fromthe OBSS. In a specific embodiment, when a PPDU is transmitted based ona trigger frame in OBSS, the wireless communication terminal maydetermine the transmission power of the PPDU to be transmitted based onthe received signal strength of the PPDU including the trigger frametransmitted from the OBSS.

In the embodiment of FIG. 7 , the OBSS receiving wireless communicationterminal is the first access point APE Specifically, the first accesspoint AP1 included in the first BSS BSS1 transmits the trigger frame tothe third station STA3, the fourth station STA4, and the fifth stationSTA5. At this time, the second station STA2 included in the second BSSBSS2 may increase the degree of spatial reuse based on the PPDUincluding the trigger frame transmitted by the first access point APESpecifically, the second station STA2 may increase the degree of spatialreuse based on the received signal strength of the PPDU including thetrigger frame transmitted by the first access point APE In a specificembodiment, when the third station STA3, the fourth station STA4, andthe fifth station STA5 transmit the UL MU PPDU to the first access pointAP1 based on the trigger frame transmitted by the first access pointAP1, the second station STA2 may transmit the UL PPDU to the secondaccess point AP2 included in the second BSS based on the PPDU includingthe trigger frame transmitted by the first access point APE

FIG. 8 shows that when a trigger frame is transmitted through thenon-legacy PPDU format from OBSS, a wireless communication terminalaccording to an embodiment of the present invention performs an SRoperation during an uplink multiplex transmission based on a triggerframe.

As described above, the wireless communication terminal may initiate theoperation of increasing the degree of spatial reuse after decoding thesignaling field of the non-legacy PPDU format (11ax PHY format). This isbecause the signaling field of the non-legacy PPDU format may indicatethat the corresponding PPDU is the UL MU PPDU. The wirelesscommunication terminal may determine whether the PPDU received based onthe signaling field of the non-legacy PPDU format is a PPDU transmittedbased on the trigger frame received previously. At this time, thesignaling field of the non-legacy PPDU format may include informationidentifying the BSS. Specifically, the signaling field of the non-legacyPPDU format may include BSS color. In a specific embodiment, thewireless communication terminal may determine whether the PPDU receivedbased on the signaling field of the non-legacy PPDU format is a PPDUtransmitted from the same BSS as the BSS where the trigger framereceived previously is transmitted. When the received PPDU istransmitted from the same BSS as the BSS where the trigger framereceived previously is transmitted, the wireless communication terminalmay initiate the operation of increasing the degree of spatial reuse.Also, the signaling field of the non-legacy PPDU format may be theHE-SIG-A field. At this time, the HE-SIG-A field includes informationrequired for interpreting the non-legacy PPDU.

Also, the wireless communication terminal may determine that the PPDUtransmitted before the corresponding PPDU includes the trigger framebased on the signaling field of the non-legacy PPDU format. As describedabove, in the case of the UL MU transmission, the access point transmitsthe trigger frame and initiates the transmission sequence. Also, thetrigger-based UL MU PPDU may be transmitted after a predetermined timefrom when the transmission of the trigger frame is completed.

Also, when the received signal strength value of the PPDU including thetrigger frame is lower than the OBSS CCA threshold value, the wirelesscommunication terminal may increase the degree of spatial reuse based onthe trigger frame. In this case, the OBSS CCA threshold value representsa reference value applied to the CCA of the PPDU transmitted from theOBSS. Specifically, when the received signal strength of the PPDUtransmitted from the OBSS is smaller than the OBSS CCA threshold value,the wireless communication terminal may determine that the channel isidle. Also, the OBSS CCA threshold value may be a Preamble Detection(PD) CCA threshold value, which is a CCA threshold value used inpreamble detection.

Also, until the UL MU PPDU transmission based on the trigger frame iscompleted, the wireless communication terminal may increase the degreeof spatial reuse based on the trigger frame. At this time, the wirelesscommunication terminal may designate the ACK frame type to betransmitted to the wireless communication terminal as a delayed ACK. Thedelayed ACK type may indicate that the ACK frame is not forced to betransmitted within a predetermined time from when the data frame istransmitted. Accordingly, the wireless communication terminal mayprotect the ACK frame to be transmitted to the wireless communicationterminal. Also, while the UL MU PPDU transmission based on the triggerframe is going, the wireless communication terminal may increase thedegree of spatial reuse based on the trigger frame. Through this, thewireless communication terminal may protect the ACK frame transmittedfrom the OBSS and the ACK frame to be transmitted to the wirelesscommunication terminal. In the embodiment of FIG. 8 , the first BSS BSS1includes a first access point AP1, a first station STA1, a third stationSTA3, a fourth station STA4, and a fifth station STA5. The second BSSBSS2 includes a second access point AP2 and a second station STA2. Thefirst access point AP1 transmits the trigger frame through thenon-legacy PPDU format to the first station STA1, the third stationSTA3, the fourth station STA4, and the fifth station STA5. The secondstation STA2 measures the received signal strength of the PPDU includingthe trigger frame transmitted by the first access point APE When thereceived signal strength of the PPDU is smaller than the OBSS PD CCAthreshold value, the second station STA2 may initiate the operation ofincreasing the degree of spatial reuse during UL MU PPDU transmissionbased on the trigger frame.

At this time, the second station STA2 may determine whether the UL MUPPDU is transmitted based on the trigger frame, based on the signalingfield of the UL MU PPDU. At this time, the second station STA2 maydetermine whether the UL MU PPDU and the PPDU including the triggerframe are transmitted from the same OBSS based on the signaling field ofthe UL MU PPDU. Specifically, the second station STA2 may determinewhether the UL MU PPDU and the PPDU including the trigger frame aretransmitted from the same OBSS based on the BSS color indicated by thesignaling field of the UL MU PPDU. Also, the second station STA2 mayincrease the degree of spatial reuse during transmission of the UL MUPPDU as described above. In another specific embodiment, the secondstation STA2 may increase the degree of spatial reuse even after thetransmission of the UL MU PPDU is completed, as described above. Theoperation of raising the degree of spatial reuse may include theembodiments described above.

FIG. 9 shows that when a trigger frame is transmitted through the legacyPPDU format from OBSS, a wireless communication terminal according to anembodiment of the present invention performs an SR operation during anuplink multiplex transmission based on a trigger frame.

When the MAC frame is transmitted through the legacy PPDU format fromthe OBSS, the wireless communication terminal may decode the MAC frameto determine whether the corresponding MAC frame is the trigger frame.Specifically, the wireless communication terminal may determine whetherthe corresponding MAC frame is a trigger frame based on the frame typefield of the MAC frame. At this time, the wireless communicationterminal may determine whether the corresponding frame is a triggerframe based on the frame type field and the subtype field of the MACframe. Also, the wireless communication terminal may determine whetherthe corresponding frame is an Inter-BSS frame by decoding the MAC headerof the MAC frame. Specifically, the wireless communication terminal maydetermine whether the frame is an Inter-BSS frame based on the addressfield of the MAC header. In a specific embodiment, the wirelesscommunication terminal may determine whether the corresponding frame isan Inter-BSS frame based on whether the receiving STA address (RA) fieldof the address field of the MAC header included in the UL MU PPDUtransmitted based on a trigger matches the transmitting STA address (TA)field of the address field of the trigger frame. The wirelesscommunication terminal may determine whether the corresponding frame isan Inter-BSS frame based on the information indicating the BSS of theframe. At this time, the information indicating the BSS may be a BSSIDfield. In addition, the information indicating the BSS may be a partialBSSID indicated by the AID field.

In the embodiment of FIG. 9 , the first BSS BSS1 includes a first accesspoint AP1, a first station STA1, a third station STA3, a fourth stationSTA4, and a fifth station STA5. The second BSS BSS2 includes a secondaccess point AP2 and a second station STA2. The first access point AP1transmits the trigger frame through the legacy PPDU format to the firststation STA1, the third station STA3, the fourth station STA4, and thefifth station STA5. The second station STA2 may decode the MAC frameincluded in the PPDU transmitted by the first access point AP1 todetermine whether the corresponding MAC frame is a trigger frame.

Specifically, the second station STA2 may determine whether thecorresponding frame is an Inter-BSS frame based on the address field ofthe MAC header. In a specific embodiment, the second station STA2 maydetermine whether the corresponding frame is an Inter-BSS frame based onwhether the RA field of the address field of the MAC header included inthe UL MU PPDU transmitted based on a trigger frame matches the TA fieldof the trigger frame. Also, the second station STA2 may determinewhether the corresponding frame is an Inter-BSS frame based on theinformation indicating the BSS of the MAC frame. At this time, theinformation indicating the BSS may be a BSSID field. In addition, theinformation indicating the BSS may be a partial BSSID indicated by theAID field. When the corresponding MAC frame is the trigger frame, thesecond station STA2 measures the received signal strength of the PPDUincluding the trigger frame transmitted by the first access point APE Ifthe received signal strength of the PPDU is smaller than the OBSS PD CCAthreshold value, the second station STA2 may initiate the operation ofincreasing the degree of spatial reuse during transmission of thetrigger-based UL MU PPDU. Other operations of the second station STA2may be the same as those of the embodiments described with reference toFIG. 8 .

FIG. 10 shows that when a non-legacy PPDU including a trigger frame anda data frame together is transmitted in OBSS, a wireless communicationterminal according to an embodiment of the present invention performs anSR operation during an uplink multiplex transmission based on a triggerframe.

When the cascading sequence proceeds in the OBSS, the wirelesscommunication terminal may increase the degree of spatial reuse duringtransmission of the UL MU PPDU transmitted based on the trigger frame.In this case, the cascading sequence is a transmission sequence in whichboth the UL MU transmission operation and the DL MU transmissionoperation are included in one transmission opportunity (TXOP). At thistime, the TXOP indicates a time period in which a specific wirelesscommunication terminal has an authority to initiate frame exchange via awireless medium. The fact that the wireless communication terminalincreases the degree of spatial reuse within the duration of the UL MUPPDU is to protect the downlink transmission to be continued after theuplink transmission. In addition, when the received signal strength ofthe UL MU PPDU transmitted based on the trigger frame is smaller than acertain threshold value, and the non-AP wireless communication terminalsthat are not access points participating in the cascading sequence areall the same, the wireless communication terminal may increase thedegree of spatial reuse even after the UL MU PPDU transmission iscompleted. Specifically, the wireless communication terminal mayincrease the degree of spatial reuse within the TXOP indicated by thetrigger frame. In addition, when the non-legacy MU PPDU is transmittedinstead of the cascading sequence, the wireless communication terminalmay increase the degree of spatial reuse within the time perioddescribed in the above-described embodiments. In this case, the timeperiod may be the duration of the trigger-based UL PPDU transmitted fromthe OBSS. Also, the time period may be a TXOP indicated by the triggerframe transmitted from the OBSS.

In the embodiment of FIG. 10 , the first BSS BSS1 includes a firstaccess point AP1, a first station STA1, a third station STA3, a fourthstation STA4, and a fifth station STA5. The second BSS BSS2 includes asecond access point AP2 and a second station STA2. The first accesspoint AP1 transmits downlink transmission data DL data and a triggerframe Trigger to the first station STA1, the third station STA3, thefourth station STA4, and the fifth station STA5. The second station STA2measures the received signal strength of the PPDU transmitted by thefirst access point APE The second station STA2 may initiate to increasethe degree of spatial reuse during transmission of a trigger-based UL MUPPDU. At this time, the trigger-based PPDU indicates the PPDUtransmitted in response to the trigger frame. Specifically, the secondstation STA2 may increase the degree of spatial reuse after decoding thesignaling field of the trigger-based UL MU PPDU. At this time, thesignaling field of the UL MU PPDU may be the HE-SIG-A field. At thistime, the second station STA2 may increase the degree of spatial reusewhile the trigger-based UL MU PPDU is transmitted. At this time, if thereceived signal strength of the UL MU PPDU is smaller than a thresholdvalue and the non-AP wireless communication terminals that are notaccess points participating in the cascading sequence are all the same,the second station STA2 may increase the degree of spatial reuse evenafter the UL MU PPDU transmission is completed. Other operations of thesecond station STA2 may be the same as those of the embodimentsdescribed with reference to FIG. 8 .

FIG. 11 shows that when a trigger-based UL MU PPDU is transmitted fromOBSS, a wireless communication terminal according to an embodiment ofthe present invention sets a NAV.

When the received signal strength of the PPDU including the triggerframe transmitted from the OBSS is smaller than a certain thresholdvalue and the wireless communication terminal receives the trigger framefor triggering the wireless communication terminal, the wirelesscommunication terminal may reset or not consider the NAV set accordingto the trigger-based UL MU PPDU transmitted from the OBSS. At this time,the specific threshold value may be an OBSS PD CCA threshold value.Since the received signal strength of the PPDU including the triggerframe transmitted from the OBSS is small, it may be determined that theinterference expected to be given to the wireless communication terminalreceiving the trigger-based UL MU PPDU is not large.

As described above, the received signal strength of the PPDU includingthe trigger frame may be smaller than a certain threshold value. At thistime, if the transmission completion time of the trigger-based UL MUPPDU indicated by the trigger frame triggering the wirelesscommunication terminal precedes the transmission completion time of thetrigger-based UL MU PPDU transmitted from the OBSS, the wirelesscommunication terminal may reset or ignore the NAV set according to thetrigger-based UL MU PPDU transmitted from the OBSS. In the embodiment ofFIG. 11 , the first BSS BSS1 includes a first station STA1 and a firstaccess point APE In addition, the second BSS BSS2 includes a secondstation STA2 and a second access point AP2. The second access point AP2transmits the PPDU including the trigger frame to the second stationSTA2. At this time, the received signal strength of the PPDU includingthe trigger frame transmitted from the second BSS measured by the firststation STA1 may be smaller than a certain threshold value. The receivedsignal strength of the PPDU including the trigger frame transmitted inthe second BSS may be smaller than a certain threshold value. Inaddition, the transmission completion time of the UL MU PPDU transmittedby the first station STA1 based on the trigger frame that the firstaccess point AP1 transmits to the first station STA1 may precede thetransmission completion time of the UL MU PPDU transmitted based on thetrigger frame transmitted from the second BSS. At this time, the firststation STA1 may reset or ignore the NAV set according to thetrigger-based UL MU PPDU transmitted from the second BSS. Through this,the wireless communication terminal may protect the ACK frame for the ULMU PPDU transmitted from the OBSS.

FIG. 12 shows an operation of a wireless communication terminalaccording to an embodiment of the present invention to increase thedegree of spatial reuse when a UL MU PPDU is transmitted from OBSS.

In the above-described embodiment, when the received signal strength ofthe PPDU including the trigger frame transmitted from the OBSS measuredby the wireless communication terminal is smaller than a certainthreshold value, the wireless communication terminal may increase thedegree of spatial reuse. At this time, the specific threshold value maybe a value determined based on the magnitude of an interferenceacceptable by the wireless communication terminal of the OBSS whenreceiving the UL MU PPDU transmitted based on the trigger frame in theOBSS. Also, the specific threshold value may be a value determined basedon the transmission power of the PPDU including the trigger frametransmitted in the OBSS. Also, the specific threshold value may be avalue determined based on the transmission power of the PPDU to betransmitted by the wireless communication terminal. Specifically, aspecific threshold value may be determined according to the followingequation.TXPWR_OBSS_AP+AcceptableReceiverInterferenceLevel_OBSS_AP−TXPWR_MY_STA

At this time, TXPWR_OBSS_AP represents the transmission power of thePPDU including the trigger frame transmitted from the OBSS. Also,AcceptableReceiverinterferenceLevel_OBSS_AP represents the amount of aninterference acceptable by the wireless communication terminal of theOBSS to receive the trigger-based UL MU PPDU. In addition, TXPWR_MY_STArepresents the transmission power of the PPDU to be transmitted by thewireless communication terminal.

Specifically, when the received signal strength of the PPDU includingthe trigger frame received by the wireless communication terminalsatisfies the following equation, the wireless communication terminalmay increase the degree of spatial reuse.RSSI_TriggerFrame_at_MY_STA<TXPWR_OBSS_AP+AcceptableReceiverinterferenceLevel_OBSS_AP−TXPWR_MY_STA

RSSI_TriggerFrame_at_MY_STA represents the received signal strength ofthe PPDU including the trigger frame transmitted from the OBSS measuredby the wireless communication terminal.

For this operation, the wireless communication terminal transmitting thetrigger frame may signal the magnitude of an interference acceptablewhen receiving the trigger-based UL MU PPDU through the trigger frame.In addition, the wireless communication terminal transmitting thetrigger frame may signal the transmission power of the PPDU includingthe trigger frame through the trigger frame. At this time, the wirelesscommunication terminal receiving the trigger frame transmitted from theOBSS may increase the degree of spatial reuse based on at least any oneof the magnitude of an interference acceptable when receiving the UL MUPPDU signaled by the wireless communication terminal transmitting thetrigger frame and the transmission power of the PPDU including thetrigger frame. Specifically, the wireless communication terminalreceiving the trigger frame transmitted from the OBSS may determinewhether the above-described equation is satisfied based on the triggerframe. In a specific embodiment, the wireless communication terminalreceiving the trigger frame transmitted from the OBSS may obtain themagnitude of an interference acceptable when receiving the UL MU PPDUtransmitted based on the trigger frame from the signaling field of thePPDU including the trigger frame. In addition, the wirelesscommunication terminal transmitting the trigger frame may signal thetransmission power of the PPDU including the trigger frame through thetrigger frame. At this time, the signaling field of the PPDU may be theHE-SIG-A field. Also, the signaling field of the PPDU may be the SpatialReuse (SR) field of the HE-SIG-A field.

The operation of increasing the degree of spatial reuse of the wirelesscommunication terminal as described above may be determined based on thechannel attenuation between a wireless communication terminal of theOBSS that transmits a trigger frame and the wireless communicationterminal. Specifically, the above-described equation may be expressed asfollows.TXPWR_MY_STA−(TXPWR_OBSS_AP−RSSI_TriggerFrame_at_MY_STA)<AcceptableReceiverinterferenceLevel_OBSS_AP

(TXPWR_OBSS_AP−RSSI_TriggerFrame_at_MY_STA) represents how much thetransmission power is attenuated while the PPDU including the triggerframe transmitted from the OBBS is transmitted to the wirelesscommunication terminal. Therefore,(TXPWR_OBSS_AP−RSSI_TriggerFrame_at_MY_STA) may be regarded as channelattenuation. In addition,(TXPWR_MY_STA−(TXPWR_OBSS_AP−RSSI_TriggerFrame_at_MY_STA)) may beregarded as the magnitude of an interference that the PPDU to betransmitted by the wireless communication terminal affects a wirelesscommunication terminal to receive the trigger-based UL MU PPDU in theOBSS. Accordingly, it may be understood that the above equationdetermines whether the magnitude of an interference occurring in awireless communication terminal to receive a trigger-based UL MU PPDU inthe OBSS is smaller than the magnitude of an interference acceptable bythe wireless communication terminal to receive a trigger-based UL MUPPDU when the wireless communication terminal transmits a PPDU.

The wireless communication terminal may adjust the transmission power ofthe PPDU to be transmitted based on the above-described equation.Specifically, when receiving the UL MU PPDU transmitted based on thetrigger frame of the OBSS, the wireless communication terminal maydetermine the transmission power of the PPDU to be transmitted based onthe magnitude of the interference acceptable by the wirelesscommunication terminal of the OBSS. Also, the wireless communicationterminal may determine the transmission power of the PPDU to betransmitted based on the transmission power of the PPDU including thetrigger frame transmitted from the OBSS. The wireless communicationterminal may increase the degree of spatial reuse while not interferingwith the reception of the UL MU PPDU in the OBSS.

Also, when the above-described equation is satisfied, the wirelesscommunication terminal may use a CCA threshold value higher than theexisting CCA threshold value. In this case, the CCA threshold valuehigher than the existing CCA threshold value may be the OBSS PD CCAthreshold value. Through the adjustment of the CCA threshold value, itis possible to prevent a collision with a transmission of anotherwireless communication terminal performing an SR operation according toa PPDU including a trigger frame transmitted from the OBSS.

In another specific embodiment, when the above-described equation issatisfied, the wireless communication terminal may determine that thecorresponding channel is idle. In another specific embodiment, when theabove-described equation is satisfied, the wireless communicationterminal may transmit the PPDU without CCA operation.

In addition, the wireless communication terminal may increase the degreeof spatial reuse while the trigger-based UL MU PPDU of the OBSS istransmitted. Specifically, the wireless communication terminal maytransmit the PPDU by adjusting the transmission power while thetrigger-based UL MU PPDU of the OBSS is transmitted. Through this, thewireless communication terminal may protect the transmission of the ACKframe to the trigger-based UL MU PPDU of the OBSS.

As described above, the wireless communication terminal may signalthrough the trigger frame at least any one of the magnitude of theinterference acceptable when receiving the trigger-based UL MU PPDU andthe transmission power of the PPDU including the trigger frame. Forconvenience of explanation, the magnitude of the interference thatacceptable when receiving the trigger-based UL MU PPDU is referred to asthe allowable interference magnitude. At this time, the wirelesscommunication terminal transmitting the trigger-based UL MU PPDU maysignal the magnitude of the allowed interference of the wirelesscommunication terminal transmitting the trigger frame through thesignaling field of the UL MU PPDU. In addition, the wirelesscommunication terminal transmitting the trigger-based UL MU PPDU maysignal the transmission power of the PPDU including the trigger framethrough the signaling field of the UL MU PPDU. At this time, thesignaling field may be the HE-SIG-A field. Specifically, the signalingfield may be a Spatial Reuse (SR) field included in the HE-SIG-A field.

At this time, the wireless communication terminal transmitting thetrigger-based UL MU PPDU may obtain the allowable interference magnitudeof the wireless communication terminal that transmits the trigger framefrom the subfield of the trigger frame. In addition, the wirelesscommunication terminal transmitting the trigger-based UL MU PPDU mayobtain the transmission power of the PPDU including the trigger framefrom the subfield of the trigger frame. Specifically, the subfield ofthe trigger frame may be a common field of the trigger frame. Forexample, the subfield of the trigger frame may be the SR field of thecommon field of the trigger frame.

Accordingly, the wireless communication terminal that increases thedegree of spatial reuse based on the PPDU including the trigger frametransmitted from the OBSS may obtain the allowable interferencemagnitude of the wireless communication terminal that transmits thetrigger frame through the signaling field of the correspondingtrigger-based UL MU PPDU. In addition, the wireless communicationterminal that increases the degree of spatial reuse based on the PPDUincluding the trigger frame transmitted from the OBSS may obtain thetransmission power of the PPDU including the trigger frame through thesignaling field of the corresponding trigger-based UL MU PPDU.

For the above-described embodiments, the wireless communication terminalmust be able to determine whether the PPDU transmitted from the OBSS isa PPDU based on a trigger frame in which the wireless communicationterminal measures the received signal strength. Specifically, thewireless communication terminal may determine whether the PPDUtransmitted from the OBSS is a PPDU based on a trigger frame in whichthe wireless communication terminal measures the received signalstrength according to whether the BSS color of the PPDU including thetrigger frame in which the wireless communication terminal measures thereceived signal strength and the BSS color of the PPDU transmitted fromthe OBSS. In another specific embodiment, after a predetermined timefrom when the transmission of the PPDU received by the wirelesscommunication terminal is completed, when a PPDU based on a triggerframe is transmitted from the OBSS, the wireless communication terminalmay determine that the PPDU received before the trigger-based PPDU isthe PPDU including the trigger frame. At this point, the predeterminedtime may be a Short Inter-Frame Space (SIFS).

At this time, the wireless communication terminal may decode the MACheader of the received PPDU and determine whether the received PPDUincludes the trigger frame. In addition, when the trigger-based PPDU istransmitted, the wireless communication terminal may determine the PPDUtransmitted before the PPDU transmission based on the trigger frame asthe PPDU including the trigger frame. Specifically, when the downlinktransmission PPDU is transmitted and the trigger-based PPDU iscontinuously transmitted, the wireless communication terminal maydetermine the PPDU transmitted before the PPDU transmission based on thetrigger frame as the PPDU including the trigger frame. In thisembodiment, the wireless communication terminal may receive thetrigger-based PPDU or decode the MAC header of the received PPDU, andthen determine whether the received PPDU includes the trigger frame.

The wireless communication terminal transmitting the trigger frame maysignal the PPDU including the trigger frame through the signaling fieldof the PPDU including the trigger frame. At this time, the wirelesscommunication terminal may determine that the PPDU received based on thesignaling field of the PPDU is a PPDU including the trigger frame. Atthis time, the signaling field may be the HE-SIG-A field. Also, thesignaling field may be the SR field of the HE-SIG-A field. At this time,the wireless communication terminal may decode the signaling field ofthe received PPDU and determine whether the received PPDU is a PPDUincluding a trigger frame. Therefore, it may be determined that the PPDUreceived a little earlier than the above-described embodiments is a PPDUincluding the trigger frame.

As in the above-described embodiments, while the trigger-based PPDU istransmitted from the OBSS, the wireless communication terminal transmitsthe PPDU based on the PPDU including the trigger frame transmitted fromthe OBSS and this may be referred to as an opportunistic adaptive CCA(OA-CCA).

FIG. 13 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

When the wireless communication terminal performs the SR operation basedon the PPDU including the trigger frame transmitted from the OBSS andtransmits the PPDU, the wireless communication terminal triggered by thetrigger frame may detect interference caused by transmission of thewireless communication terminal and determine that the correspondingchannel is busy. Accordingly, the wireless communication terminaltriggered by the trigger frame may not be able to transmit thetrigger-based PPDU. To prevent this, the wireless communication terminalmay perform the SR operation within the duration of the PPDU includingthe trigger frame transmitted from the OBSS. Specifically, the wirelesscommunication terminal may transmit the PPDU based on the SR operationwithin the duration of the PPDU including the trigger frame transmittedfrom the OBSS.

At this time, the wireless communication terminal may change the SRoperation according to the type of the PPDU transmitted from the OBSS.Specifically, when the PPDU including the trigger frame transmitted fromthe OBSS is a non-legacy PPDU for extended range transmission, thewireless communication terminal may not transmit the PPDU based on theSR operation while the PPDU including the trigger frame is transmitted.In addition, when the PPDU including the trigger frame transmitted fromthe OBSS is a non-legacy PPDU for a single user (SU) transmission, thewireless communication terminal may not transmit the PPDU based on theSR operation while the PPDU including the trigger frame is transmitted.The duration of non-legacy PPDUs for extended range transmission andnon-legacy PPDUs for single user transmission may not be longer thanthat of other types of PPDUs.

In addition, if the PPDU including the trigger frame transmitted fromthe OBSS is a non-legacy PPDU for a multi-user (MU), the wirelesscommunication terminal may transmit the PPDU based on the SR operationwithin the duration of the PPDU including the trigger frame. Asdescribed above, the signaling field of a PPDU may indicate that thecorresponding PPDU includes a trigger frame. Specifically, a specificvalue of the SR field of HE-SIG-A may indicate that it includes acorresponding PPDU trigger frame. Also, the signaling field of the PPDUmay indicate that the corresponding PPDU is a PPDU for downlinktransmission. At this time, the signaling field of the PPDU is a PPDUfor downlink transmission, and when the SR field has a specific value,the SR field may indicate that corresponding PPDU includes triggerframe. At this time, when the PPDU is a PPDU for uplink transmission,the specific value of the SR field may be used for another purpose.

FIG. 14 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

The wireless communication terminal may adjust the transmission power ofthe PPDU to be transmitted based on the equation described withreference to FIG. 12 . Specifically, when receiving the UL MU PPDUtransmitted based on the trigger frame of the OBSS, the wirelesscommunication terminal may determine the transmission power of the PPDUto be transmitted based on the magnitude of the interference acceptableby the wireless communication terminal of the OBSS. Also, the wirelesscommunication terminal may determine the transmission power of the PPDUto be transmitted based on the transmission power of the PPDU includingthe trigger frame transmitted from the OBSS. At this time, the wirelesscommunication terminal transmitting the trigger frame may signal atleast one of the allowable interference magnitude and the transmissionpower of the trigger frame through the trigger frame as described withreference to FIG. 12 . Specifically, a wireless communication terminaltransmitting a trigger frame may transmit spatial reuse field parameters(SRP) through a trigger frame. At this time, the value of the SRP may bedetermined based on the allowable interference magnitude and thetransmission power of the trigger frame. Specifically, the SRP may bethe sum of the transmission power of the PPDU including the triggerframe and the allowable interference magnitude of the wirelesscommunication terminal transmitting the trigger frame. In addition, thewireless communication terminal transmitting the trigger-based PPDU mayinsert the SRP into the signaling field of the PPDU. The wirelesscommunication terminal may obtain the SRP from the trigger-based PPDUtransmitted from the OBSS and determine the transmission power of thePPDU to be transmitted based on the SRP. Specifically, the wirelesscommunication terminal may determine the transmission power of the PPDUto be transmitted according to the following equation.TXPWR_MY_STA<SRP−RSSI_TriggerFrame_at_MY_STASRP=TXPWR_OBSS_AP+AcceptableReceiverInterferenceLevel_OBSS_AP

At this time, TXPWR_OBSS_AP represents the transmission power of thePPDU including the trigger frame transmitted from the OBSS. Also,AcceptableReceiverinterferenceLevel_OBSS_AP indicates an allowableinterference magnitude, which is the magnitude of interferenceacceptable by the wireless communication terminal of the OBSS to receivethe trigger-based UL MU PPDU. In addition, TXPWR_MY_STA represents thetransmission power of the PPDU to be transmitted by the wirelesscommunication terminal. In addition, RSSI_TriggerFrame_at_MY_STArepresents the received signal strength of the PPDU including thetrigger frame transmitted from the OBSS measured by the wirelesscommunication terminal.

Therefore, the wireless communication terminal may determine thetransmission power based on the received signal strength of the PPDUincluding the trigger frame transmitted from the OBSS and the SRP valueindicated by the signaling field of the trigger-based PPDU transmittedfrom the OBSS.

In the embodiment of FIG. 14 , the first BSS BSS1 includes a firststation STA1 which is not an access point and a second station STA2which is an access point. The second BSS BSS2 includes a fourth stationSTA4 which is an access point and a third station STA3 which is not anaccess point. The second station STA2 transmits the trigger frame to thefirst station STA1. At this time, the second station STA2 may insert theSRP into the trigger frame. The third station STA3 measures the receivedsignal strength of the PPDU including the trigger frame transmitted bythe second station STA2. Also, the first station STA1 transmits thetrigger-based UL PPDU. At this time, the first station STA1 may insertthe SRP into the signaling field of the trigger-based UL PPDU. The thirdstation STA3 may obtain the SRP value from the signaling field of thetrigger-based UL PPDU transmitted by the first station STA1. When thetransmission power value of the PPDU to be transmitted from the thirdstation STA3 to the fourth station STA4 is smaller than the valueobtained by subtracting the received signal strength of the PPDUincluding the trigger frame transmitted from the second station STA2from the value of the SRP, the third station STA3 may transmit the PPDUto the fourth station STA4.

The magnitudes of transmission power and interference may be valuesnormalized over the 20 MHz frequency bandwidth. For example,TXPWR=power−10*log(BW/20 MHz). Thus, the SRP may be a normalized valueover the 20 MHz frequency bandwidth. Accordingly, the wirelesscommunication terminal may scale the transmission power value of thePPDU to be transmitted according to the frequency bandwidth used by thePPDU to be transmitted and apply it to the above-described equation.

When receiving a wireless signal, the wireless communication terminalmay process the received signal in a physical layer and a MAC layer. Atthis time, the interface between the physical layer and the MAC layer iscalled a primitive. In addition, the operation of the physical layer ofthe wireless communication terminal may be performed by the PHY SublayerManagement Entity (PLME). In addition, the operation of the MAC layer ofthe wireless communication terminal may be performed by the MAC SublayerManagement Entity (MLME). At this time, for the embodiments describedabove, RXVECTOR of the primitive may include at least one of a spatialreuse parameter (SRP), a TXOP duration, and a BSS color.

FIG. 15 shows an SR operation of a wireless communication terminalaccording to an embodiment of the present invention when a legacy PPDUincluding a trigger frame is transmitted from the OBSS.

As described with reference to FIG. 14 , the wireless communicationterminal may transmit the PPDU according to the SR operation based onthe received signal strength of the PPDU including the trigger frametransmitted from the OBSS and the value of the SRP indicated by thetrigger-based PPDU. Specifically, the wireless communication terminalmay transmit the PPDU by adjusting the transmission power based on thereceived signal strength of the PPDU including the trigger frametransmitted from the OBSS and the value of the SRP indicated by thetrigger-based PPDU. However, when the PPDU including the trigger frameis a legacy PPDU, the wireless communication terminal is required todecode the MAC frame of the corresponding PPDU to determine whether thecorresponding PPDU includes the trigger frame. In addition, when the BSSindicated by the signaling field of the PPDU is different from the BSSindicated by the address field of the MAC header, the wirelesscommunication terminal is required to decode the MAC frame of thecorresponding PPDU. At this time, the wireless communication terminalmay obtain the value of the SRP from the trigger frame. The wirelesscommunication terminal may transmit the PPDU by adjusting thetransmission power based on the SRP value obtained from the triggerframe of the OBSS. Specifically, as described above, the wirelesscommunication terminal may adjust the transmission power of the PPDU tobe transmitted so as to satisfy the following equation.TXPWR_MY_STA<SRP−RSSI_TriggerFrame_at_MY_STA

At this time, the wireless communication terminal may transmit the PPDUby adjusting the transmission power at the time of obtaining the SRPvalue. In another specific embodiment, the wireless communicationterminal may initiate the transmission of the PPDU by adjusting thetransmission power at the end of the transmission of the PPDU includingthe trigger frame transmitted from the OBSS. In the embodiment of FIG.15 , it is shown that at the end of the transmission of the PPDUincluding the trigger frame transmitted from the OBSS, the wirelesscommunication terminal adjusts the transmission power to transmit thePPDU. In another specific embodiment, when the PPDU including thetrigger frame is a legacy PPDU, the wireless communication terminal maytransmit the PPDU by adjusting the transmission power at the time whenthe corresponding PPDU identifies the trigger frame transmitted from theOBSS. In these embodiments, the wireless communication terminal maytransmit the PPDU based on the SR operation at a time point earlier thanthe embodiment described with reference to FIG. 14 .

FIG. 16 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation based on acontention procedure when a PPDU including a trigger frame istransmitted from the OBSS.

As described above, the wireless communication terminal may transmit thePPDU based on the PPDU including the trigger frame transmitted from theOBSS during the trigger-based PPDU transmission procedure from the OBSS.Specifically, the wireless communication terminal may transmit a PPDUunder the condition of the equation described in the embodiment of FIG.12 . In the specific embodiment, the wireless communication terminal maytransmit the PPDU by adjusting the transmission power according to theequations described in the embodiments of FIGS. 12 and 14 .

One or a plurality of wireless communication terminals in the UL MUtransmission procedure in the OBSS may transmit the PPDU based on the SRoperation. When a plurality of wireless communication terminals transmitPPDUs based on the SR operation, a collision may occur betweentransmissions of different wireless communication terminals. Further,when a plurality of wireless communication terminals transmit PPDUs,interference exceeding the magnitude of the interference acceptable bythe access point of the OBSS may occur.

In the embodiment of FIG. 16 , the first BSS BSS1 includes a firststation STA1 other than an access point and a second station STA2 whichis an access point. In addition, the second BSS BSS2 also includes athird station STA3 other than an access point, a fourth station STA4which is an access point, and a fifth station STA5 other than an accesspoint. Also, the third BSS BSS 3 includes the sixth station STA 6. Whenthe third to sixth stations STA3 to STA6 transmit PPDUs at the sametime, transmission of the third station STA3 to the sixth station STA6may fail due to a transmission collision. In addition, the third stationSTA3 and the fifth station STA5 may simultaneously transmit PPDUs to thefourth station STA4. In addition, when two of the third to sixthstations STA3 to STA6 transmit PPDUs, interference greater than themagnitude of the interference acceptable by the second station STA2 mayoccur. Accordingly, the second station STA2 may not receive the PPDUfrom the first station STA1. To solve this problem, when a wirelesscommunication terminal transmits a PPDU based on the SR operation in theUL MU transmission procedure in the OBSS, the wireless communicationterminal may access the channel based on a backoff procedure.

When the wireless communication terminal transmits the PPDU based on theSR operation in the UL MU transmission procedure in the OBSS, thewireless communication terminal may reduce the backoff counter by apredetermined time period when the channel is idle for a predeterminedtime period or more. At this time, a certain time period may be referredto as a slot. At this time, the wireless communication terminal may usethe backoff counter value used when accessing the channel through theDCF and the EDCAF as the backoff counter value. Further, in order todetermine whether the channel is idle, the wireless communicationterminal may use Energy Detect (ED). Also, the wireless communicationterminal may determine whether the channel is idle by determiningwhether there is a PPDU having an strength equal to or greater than athreshold value. In this case, the threshold value may be a value largerthan the existing minimum receive sensitivity. For example, the wirelesscommunication terminal may perform a CCA operation based on a colorcode, on the basis of the OBSS PD CCA threshold value used as thethreshold value for Preamble Detection (PD) of the OBSS in the colorcode based CCA. When an inter-BSS PPDU is transmitted, the color codebased CCA may indicate that the wireless communication terminal uses anOBSS PD CCA threshold value higher than the minimum receive sensitivity.At this time, the wireless communication terminal may determine whetherthe received PPDU is inter-BSS or intra-BSS based on the BSS color orthe MAC address.

In another specific embodiment, the wireless communication terminal mayperform CCA using a threshold value that is higher than the OBSS PD CCAthreshold value. In another specific embodiment, the wirelesscommunication terminal may reduce the backoff counter without CCA.Specifically, the wireless communication terminal may reduce the backoffcounter over time regardless of whether the channel is idle or not. Asdescribed above, the wireless communication terminal may use the backoffcounter value used when accessing the channel through the DCF and theEDCF as the backoff counter value. Through these embodiments, thewireless communication terminal may obtain a large number oftransmission opportunities during the UL PPDU transmission procedure inthe OBSS.

In addition, when the wireless communication terminal transmits the PPDUbased on the SR operation in the UL PPDU transmission procedure in theOBSS, the wireless communication terminal may determine whether theenergy level of the channel to which the PPDU is transmitted changes.Specifically, when the wireless communication terminal transmits thePPDU based on the SR operation in the UL MU transmission procedure fromthe OBSS, the wireless communication terminal may determine whether thechange of the energy level of the channel through which the PPDU istransmitted is equal to or greater than a reference value. When thewireless communication terminal detects a change in the energy level ofthe channel through which the PPDU is to be transmitted, the wirelesscommunication terminal may stop the PPDU transmission. When there is achange in the energy level of the channel to which the PPDU istransmitted, during the OBSS UL PPDU transmission procedure, this isbecause another wireless communication terminal may initiate the PPDUtransmission based on the SR operation. In addition, only a wirelesscommunication terminal whose backoff counter value is less than or equalto a specific value at the initiation of OA-CCA may transmit a PPDUbased on the SR operation. Specifically, only a wireless communicationterminal whose backoff counter value is less than or equal to a specificvalue at the initiation of UL PPDU transmission in the OBSS may transmita PPDU based on the SR operation. For example, when only a wirelesscommunication terminal having a backoff counter value of 1 or less atthe initiation of UL PPDU transmission in the OBSS transmits a PPDU, itis possible to prevent a plurality of wireless communication terminalsfrom performing transmission simultaneously. Also, if the wirelesscommunication terminal determines the transmission power of the PPDU tobe transmitted during the UL PPDU transmission procedure in the OBSS, itmay not be allowed to change the transmission power thereafter. Afterthe wireless communication terminal determines the transmission power ofthe PPDU, if the transmission power is changed according to the PPDUtransmission condition, this is because more wireless communicationterminals simultaneously transmit PPDUs. The wireless communicationterminal may minimize the interference that may occur in receiving theUL PPDU in the OBSS through these embodiments.

Also, when the wireless communication terminal attempts to transmit PPDUduring the UL PPDU transmission procedure in the OBSS and then stops,the wireless communication terminal may regard the corresponding channelas being busy during the remaining UL PPDU transmission duration.Through this, the wireless communication terminal may protect the ULPPDU transmission in the OBSS.

FIG. 17 shows an operation of a wireless communication terminal to set aNAV according to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

When the PPDU including the trigger frame is transmitted from the OBSSand the wireless communication terminal transmits the PPDU based on theSR operation, the wireless communication terminal may not set the NAVaccording to the trigger frame. Further, when the wireless communicationterminal does not receive the PPDU including the trigger frametransmitted from the OBSS, the wireless communication terminal may notset the NAV according to the trigger frame.

When the wireless communication terminal receives the trigger-based PPDUtransmitted from the OBSS, the PPDU may be transmitted based on the SRoperation as in the above-described embodiments. At this time, when thecondition that the wireless communication terminal transmits the PPDUbased on the SR operation is not satisfied, the wireless communicationterminal may set the NAV based on the signaling field of thetrigger-based PPDU. At this time, the signaling field may be the TXOPDuration field of the HE-SIG-A field. Further, when the condition thatthe wireless communication terminal transmits the PPDU based on the SRoperation is not satisfied, the wireless communication terminal may notperform the CCA based on the color code while the trigger-based PPDU istransmitted from the OBSS. Specifically, while the trigger-based PPDU istransmitted from the OBSS, the wireless communication terminal may use ageneral CCA threshold value without using the OBSS PD CCA thresholdvalue. This is because the PPDU transmission of the wirelesscommunication terminal may cause interference, which is larger than theinterference magnitude acceptable by the wireless communication terminalreceiving the trigger-based PPDU in the OBSS, to the wirelesscommunication terminal receiving the trigger-based PPDU in the OBSS.

When the wireless communication terminal interferes with the receptionof the access point of the OBSS receiving the trigger-based PPDU, aplurality of wireless communication terminals may fail the transmissionto the access point of the OBSS. In addition, like the second stationSTA2 in the embodiment of FIG. 17 , the wireless communication terminalmay receive the legacy preamble of the trigger-based PPDU transmittedfrom the OBSS, and may not receive the non-legacy signaling field. Inthis case, the wireless communication terminal may perform CCA based onthe minimum receive sensitivity.

In addition, when the information for determining whether the conditionthat the wireless communication terminal transmits the PPDU based on theSR operation is satisfied is insufficient, the wireless communicationterminal may not transmit the PPDU based on the SR operation. At thistime, the wireless communication terminal may not perform the CCA basedon the color code while the trigger-based PPDU is transmitted from theOBSS. Specifically, while the trigger-based PPDU is transmitted from theOBSS, the wireless communication terminal may use a general CCAthreshold value without using the OBSS PD CCA threshold value. At thistime, when the information for determining whether to satisfy thecondition for transmitting the PPDU based on the SR operation isinsufficient, a case where the trigger frame is not received may beincluded.

In another specific embodiment, the wireless communication terminal maynot perform the CCA based on the color code while the trigger-based PPDUis transmitted from the OBSS. As in the previously describedembodiments, while the trigger-based PPDU is transmitted from the OBSS,the wireless communication terminal may transmit the PPDU inconsideration of the reception of the trigger-based PPDU. At this time,this is because when a plurality of wireless communication terminalsgenerate interference, the reception of the trigger-based PPDU in theOBSS may fail.

FIG. 18 shows an operation of a wireless communication terminal to set aNAV according to an embodiment of the present invention when a PPDUincluding a trigger frame is transmitted from the OBSS.

When the NAV is set and the OA-CCA condition is satisfied, the wirelesscommunication terminal may reset the set NAV. The wireless communicationterminal may reset the NAV and then transmit the PPDU according to theOA-CCA operation. Further, the wireless communication terminal may setthe NAV according to the BSS indicated by the trigger-based PPDU.Specifically, when the BSS indicated by the frame for setting the NAVmatches the BSS indicated by the UL PPDU of the OBSS to which the OA-CCAis applicable, the wireless communication terminal may reset the NAV.

The wireless communication terminal may determine whether the BSS ismatched based on the BSS color. Specifically, by comparing the BSS colorindicated by the PPDU for setting the NAV with the BSS color indicatedby the UL PPDU of the OBSS to which the OA-CCA applicable, the wirelesscommunication terminal may determine whether the BSS is matched. Forthis purpose, the wireless communication terminal may store the BSScolor indicated by the PPDU for setting the NAV. In another specificembodiment, the wireless communication terminal may determine whetherthe BSS is matched based on the BSS color and the MAC address.Specifically, the wireless communication terminal may identify the BSSIDof the BSS corresponding to the BSS color. At this time, the wirelesscommunication terminal may determine whether the BSS indicated by theBSSID of the frame for setting the NAV matches the BSS indicated by theBSS color indicated by the UL PPDU of the OBSS to which the OA-CCA isapplicable. In another specific embodiment, when the wirelesscommunication terminal receives all the PPDUs continuously transmittedfrom one TXOP, it may be determined that the BSS indicated by the PPDUfor setting the NAV and the BSS indicated by the UL PPDU of the OBSS towhich the DA-CCA is applicable are the same. When the wirelesscommunication terminal may not identify the BSS indicated by the framefor setting the NAV, even if the OA-CCA may be applied to the UL PPDU ofthe OBSS, the wireless communication terminal may not be allowed tocancel the NAV setting. This is because the NAV set by the frametransmitted from the BSS different from the BSS indicated by the UL PPDUof the OBSS to which the OA-CCA is applicable may be released by theOA-CCA operation.

In the embodiment of FIG. 18 , the access point and the plurality ofstations perform the cascading transmission sequence in the first BSSwith the BSS color value of 1. At this time, the second BSS overlappingwith the first BSS and having the BSS color value of 2 includes thefirst station STA1 and the second station STA2. The first station STA1and the second station STA2 set the NAV based on the DL MU PPDUtransmitted from the first BSS. At this time, it is assumed that thesecond station STA2 identifies only the inter-BSS indicated by the DL MUPPDU and does not identify the specific BSSID or BSS color indicated bythe DL MU PPDU. While the first UL MU PPDU is transmitted from thesecond BSS, the first station STA1 and the second station STA2 determinethat the OA-CCA condition is not satisfied. While the second UL MU PPDUis transmitted from the second BSS, the first station STA1 and thesecond station STA2 determine that the OA-CCA condition is satisfied. Atthis time, the first station STA1 determines that the BSS indicated bythe UL MU PPDU is the same as the BSS indicated by the DL MU PPDU forsetting the NAV is set, and releases the NAV. However, since the secondstation STA2 does not explicitly identify the BSS indicated by the DL MUPPDU for setting the NAV, the second station STA2 does not release theNAV. Therefore, the first station STA1 transmits the PPDU based on theOA-CCA operation while the second UL MU PPDU is transmitted from thesecond BSS. Also, the second station STA2 does not transmit the PPDUwhile the second UL MU PPDU is transmitted from the second BSS.

Although the embodiments described with reference to FIG. 18 aredescribed through the cascading sequence, UL MU transmissions within oneTXOP may also be applied to consecutive transmission sequences.

FIG. 19 shows that a wireless communication terminal according to anembodiment of the present invention transmits a PPDU by adjustingtransmission power in an SR operation.

The wireless communication terminal may perform adjustment inconjunction with the OBSS CCA threshold value and the transmission powerwhile the OBSS PPDU is transmitted. In this case, the OBSS CCA thresholdvalue may be an OBSS PD CCA threshold value. When the transmission powerof the PPDU to be transmitted by the wireless communication terminal islow, the influence of the transmission of the wireless communicationterminal on the wireless communication terminal of the OBSS isrelatively small. Therefore, when the transmission power of the PPDU tobe transmitted by the wireless communication terminal is low, thewireless communication terminal may use a relatively high OBSS CCAthreshold value. Also, as the OBSS CCA threshold value is higher, thetransmission of the wireless communication terminal may more likelyaffect the wireless communication terminal of the OBSS. Therefore, whenthe OBSS CCA threshold value is relatively high, the wirelesscommunication terminal may transmit the PPDU with a relatively lowtransmission power.

Specifically, when the wireless communication terminal detects thereception of the OBSS PPDU and applies the OBSS CCA threshold value, thewireless communication terminal may transmit the PPDU by adjusting thetransmission power based on the OBSS CCA threshold value. In FIG.19(a)-2, the wireless communication terminal detects PPDUs transmittedfrom the OBSS. The wireless communication terminal may perform the CCAby applying the OBSS PD CCA threshold value. At this time, the wirelesscommunication terminal adjusts the transmission power of the PPDU to betransmitted based on the OBSS PD CCA threshold value. The wirelesscommunication terminal transmits the PPDU with the adjusted transmissionpower.

According to the specific conditions, the wireless communicationterminal may transmit the PPDU with the transmission power which is notadjusted for the SR operation while the OBSS PPDU is transmitted. Atthis time, the power which is not adjusted for the SR operation may be apredetermined transmission power. In yet another specific embodiment,the power which is not adjusted for SR operation may be the maximumtransmission power that the wireless communication terminal may output.In addition, the predetermined transmission power may be designated bythe access point.

In addition, when the wireless communication terminal does not detectthe reception of the OBSS PPDU, the wireless communication terminal maytransmit the PPDU with the transmission power corresponding to the MYBSSCCA threshold value. At this time, the MYBSS CCA threshold valueindicates a reference value applied to the CCA of the PPDU transmittedfrom the BSS including the wireless communication terminal. In thiscase, the MYBSS CCA threshold value may be the PD CCA threshold valueused in the PD. Specifically, when the received signal strength of thePPDU transmitted from the BSS including the wireless communicationterminal is smaller than the CCA threshold value, the wirelesscommunication terminal may determine that the corresponding channel isidle. Specifically, when the wireless communication terminal does notdetect the reception of the OBSS PPDU, the wireless communicationterminal may transmit the PPDU without adjusting the transmission poweraccording to the MYBSS CCA threshold value. The MYBSS CCA thresholdvalue is not a relatively high CCA threshold value like the OBSS CCAthreshold value. FIG. 19(a) shows that the PPDU is transmitted at atransmission power corresponding to the MYBSS PD CCA threshold valuewhen the wireless communication terminal fails to detect the PPDUtransmitted from the OBSS. At this time, the transmission powercorresponding to the MYBSS CCA threshold value may be a well knownvalue. In addition, the transmission power corresponding to the MYBSSCCA threshold value may be a static value. Also, the transmission powercorresponding to the MYBSS CCA threshold value may be the maximumtransmission power that the wireless communication terminal may use.

When a PPDU transmitted through a SR operation is received, and the PPDUis transmitted in response to the PPDU received by the wirelesscommunication terminal, when the SR operation is not considered, thecorresponding PPDU transmissions may interfere with the transmission ofPPDUs transmitted from the OBSS. In the embodiment of FIG. 19(b), thenon-legacy access point HE A AP may perform the SR operation while thenon-legacy station B-1 transmits the PPDU. At this time, the non-legacyaccess point HE A AP may transmit the DL MU PPDU by adjusting thetransmission power. The non-legacy stations A-1 and A-2 included in thesame BSS as the non-legacy access point HE A AP may transmit the UL MUPPDU based on the DL MU PPDU. At this time, when the non-legacy stationsA-1 and A-2 do not adjust the transmission power to an appropriatemagnitude, the transmission of the PPDU of the non-legacy stations A-1and A-2 may interfere with the transmission of the PPDU of thenon-legacy station B-1. Therefore, a wireless communication terminalthat needs to receive the PPDU transmission of the non-legacy stationB-1 may not receive the PPDU transmitted by the non-legacy station B-1.

Also, it may be assumed that a wireless communication terminal obtains aTXOP based on a relatively high OBSS CCA threshold value and transmits aPPDU with a relatively low transmission power corresponding to an OBSSCCA threshold value. At this time, when the wireless communicationterminal transmits the PPDU with a transmission power higher than thetransmission power initially used in the transmission in the same TXOP,a large interference not acceptable by the wireless communicationterminal of the OBSS may occur. Therefore, within the TXOP to which theSR operation is applied, the wireless communication terminal may operateas follows.

The wireless communication terminal may transmit the PPDU by adjustingthe transmission power according to the OBSS CCA threshold value in theTXOP obtained based on the OBSS CCA threshold value. At this time, theTXOP may include a cascading sequence. In addition, the TXOP may includea consecutive UL MU transmission procedure. In a specific embodiment,the wireless communication terminal may transmit the PPDU by adjustingthe transmission power according to the OBSS CCA threshold value, andtransmit the next PPDU by adjusting the transmission power according tothe OBSS CCA threshold value in the same TXOP. Also, when a wirelesscommunication terminal receiving a PPDU whose transmission power isadjusted transmits a response PPDU for the PPDU whose transmission poweris adjusted within the same TXOP, the wireless communication terminalreceiving the PPDU whose transmission power is adjusted may transmit theresponse PPDU by adjusting the transmission power based on the OBSS CCAthreshold value. For convenience of description, a wirelesscommunication terminal that transmits a PPDU whose transmission power isadjusted is referred to as a transmitting wireless communicationterminal, and a wireless communication terminal receiving the PPDU whosetransmission power is adjusted is referred to as a receiving wirelesscommunication terminal. At this time, even if the receiving wirelesscommunication terminal does not perform the CCA according to the OBSSCCA threshold value, the receiving wireless communication terminal maytransmit the response PPDU by adjusting the transmission power based onthe OBSS CCA threshold value. In addition, even if the receivingwireless communication terminal performs the CCA according to the OBSSCCA threshold value, the receiving wireless communication terminal maytransmit the response PPDU by adjusting the transmission power based onthe OBSS CCA threshold value. The OBSS CCA threshold value used by thereceiving wireless communication terminal to adjust the transmissionpower may be the OBSS CCA threshold value used by the transmittingwireless communication terminal. At this time, the receiving wirelesscommunication terminal may obtain the OBSS CCA threshold value used bythe transmitting wireless communication terminal based on the signalingfield of the PPDU whose transmission power is adjusted. Specifically,the receiving wireless communication terminal may obtain thetransmission power of the corresponding PPDU from the signaling field ofthe PPDU whose transmission power is adjusted and obtain the OBSS CCAthreshold value used by the transmitting wireless communication terminalbased on the obtained transmission power. At this time, the signalingfield may be a TCI field described below. In yet another specificembodiment, the OBSS CCA threshold value may be a predetermined OBSS CCAthreshold value in the receiving wireless communication terminal.

Therefore, when the wireless communication terminal transmits the PPDUby adjusting the transmission power according to the OBSS CCA thresholdvalue in the TXOP obtained based on the OBSS CCA threshold value, thetransmission power of the PPDU transmitted within the corresponding TXOPmay be adjusted according to the OBSS CCA threshold value. In FIG.19(a)-3, the wireless communication terminal obtains the TXOP based onthe OBSS PD CCA threshold value. At this time, the transmission power ofthe PPDU transmitted in the corresponding TXOP is adjusted based on theOBSS PD CCA threshold value.

At this time, the signaling field of the PPDU may indicate that thetransmission power is adjusted. Specifically, the signaling field of thePPDU may include a TXPWR Control Indication (TCI) field indicating thatthe transmission power is adjusted. At this time, the TCI field mayinclude the transmission power of the corresponding PPDU. Specifically,the signaling field of the PPDU may include at least one of L-STF,L-LTF, L-SIG, RL-SIG, and HE-SIG-A as shown in FIG. 19(c).

When the wireless communication terminal transmits the trigger-based ULMU PPDU, the wireless communication terminal may transmit the UL MU PPDUby adjusting the transmission power so that the access point may receivethe UL MU PPDU. Specifically, the wireless communication terminal otherthan the access point may adjust the transmission power of the UL MUPPDU based on the frequency bandwidth of the frequency band allocated bythe wireless communication terminal. Specifically, when the firstfrequency bandwidth is larger than the second frequency band, thewireless communication terminal may use a smaller transmission powerwhen transmitting the UL MU PPDU through the second frequency bandwidththan when transmitting the UL MU PPDU through the first frequencybandwidth. This is because if the frequency bandwidth through which thewireless communication terminal transmits the PPDU is small, thewireless communication terminal may transmit it to a far distance at thesame transmission power. For example, when the transmission power atwhich the wireless communication terminal transmits the PPDU to theaccess point through the frequency band having the frequency bandwidthof 20 MHz is X, if a wireless communication terminal transmits a PPDU toan access point at the transmission power X through a frequency bandhaving a frequency bandwidth of 10 MHz, the received signal strength(RSSI) of the PPDU received by the access point may be unnecessarilyhigh. Therefore, when a wireless communication terminal transmits a PPDUto an access point through a frequency band of 10 MHz, the PPDU may betransmitted to the access point with a transmission power less than thetransmission power used when the PPDU is transmitted through a frequencyband having a frequency bandwidth of 20 MHz.

FIG. 20 shows that when a UL MU PPDU is transmitted in from OBSS, awireless communication terminal according to an embodiment of thepresent invention performs an SR operation while protecting an ACK framefor an UL MU PPDU transmitted from the OBSS.

As described above, the wireless communication terminal may transmit thePPDU by adjusting the transmission power while the trigger-based PPDU ofthe OBSS is transmitted. That is, the wireless communication terminalmay transmit the PPDU by adjusting the transmission power within theduration of the trigger-based PPDU of the OBSS. Through this, thewireless communication terminal may protect the transmission of the ACKframe for the trigger-based PPDU. At this time, when the wirelesscommunication terminal accesses the channel based on the contentionprocedure and transmits the PPDU based on the SR operation, the wirelesscommunication terminal may transmit the PPDU based on the SR operationeven after the transmission of the trigger-based PPDU is completed inthe OBSS. It may be regarded that the wireless communication terminaldetermines that the wireless communication terminal receiving the ACKframe through the contention procedure is located at a certain distanceor more.

FIG. 21 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

As described above, the wireless communication terminal may transmit thePPDU based on the SR operation. Specifically, the wireless communicationterminal may operate as follows.

The wireless communication terminal receives the first PPDU (S2101). Atthis time, the wireless communication terminal transmits the second PPDUbased on the BSS information indicated by the first PPDU (S2103). Atthis time, the BSS information may be at least one of a BSS color and aBSSID. The BSS indicated by the first PPDU may be different from the BSSincluding the wireless communication terminal. Specifically, the firstPPDU may be a PPDU transmitted from the OBSS. Also, the first PPDU mayinclude a trigger frame. At this time, if the wireless communicationterminal measures the received signal strength of the first PPDU andtransmits the second PPDU after the transmission of the first PPDU iscompleted, the transmission power of the second PPDU may be adjustedbased on the received signal strength of the first PPDU. Specifically,the wireless communication terminal may transmit the second PPDUaccording to the transmission conditions described with reference toFIG. 12 and FIG. 14 . Also, the wireless communication terminal maytransmit the second PPDU based on the SR operation while the first PPDUis transmitted. At this time, the wireless communication terminal maychange the SR operation according to the type of the first PPDU.Specifically, the wireless communication terminal may transmit thesecond PPDU according to the embodiment illustrated in FIG. 13 .

Also, the wireless communication terminal may receive the third PPDUwhich is the uplink PPDU transmitted based on the trigger frame. At thistime, the wireless communication terminal may decode the signaling fieldof the third PPDU and then transmit the second PPDU based on thesignaling field of the third PPDU. Specifically, the wirelesscommunication terminal may decode the signaling field of the third PPDUto determine whether the third PPDU is transmitted based on the secondPPDU. At this time, the wireless communication terminal may adjust thetransmission power of the second PPDU based on whether the third PPDU istransmitted based on the second PPDU. Specifically, the wirelesscommunication terminal may determine whether the BSS color indicated bythe signaling field of the third PPDU is equal to the BSS color of theBSS including the wireless communication terminal. At this time, basedon whether the BSS color indicated by the signaling field of the thirdPPDU is equal to the BSS color of the BSS including the wirelesscommunication terminal, the wireless communication terminal maydetermine whether the third PPDU is transmitted based on the first PPDU.Also, the signaling field may be the HE-SIG-A field described above. Thespecific operation of the wireless communication terminal may be thesame as the embodiment described with reference to FIG. 8 through FIG.10 .

In addition, the wireless communication terminal may set a value of anetwork allocation vector (NAV) according to the BSS indicated by thethird PPDU. Specifically, the wireless communication terminal may set avalue of a network allocation vector (NAV) according to the BSSindicated by the third PPDU according to the embodiments described withreference to FIGS. 11, 17, and 18 . At this time, the setting of the NAVvalue includes resetting the NAV.

The signaling field of the third PPDU may include a parameter determinedbased on the magnitude of interference acceptable by the wirelesscommunication terminal transmitting the first PPDU when receiving thethird PPDU and the transmission power of the first PPDU. At this time,the wireless communication terminal may adjust the transmission power ofthe second PPDU based on the parameter value and the received signalstrength. At this time, the parameter value may be a normalized valueover the 20 MHz frequency bandwidth. Specifically, the parameter may bethe SRP described above.

Also, when the BSS indicated by the first PPDU is different from the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may perform CCA by applying an overlapped BSS CCAthreshold value which is larger than the CCA threshold value applied tothe PPDU transmitted from the BSS including the wireless communicationterminal. At this time, the wireless communication terminal maydetermine the transmission power of the second PPDU in conjunction withthe threshold value of the OBSS CCA. Specifically, when the wirelesscommunication terminal transmits the fourth PPDU in the TXOP obtainedwhen transmitting the second PPDU, it is possible to adjust thetransmission power of the fourth PPDU in conjunction with the OBSS CCAthreshold value. In addition, the wireless communication terminalreceiving the second PPDU whose transmission power is adjusted maytransmit the PPDU by adjusting the transmission power within thecorresponding TXOP. At this time, the wireless communication terminalreceiving the second PPDU whose transmission power is adjusted maydetermine the transmission power of the PPDU to be transmitted inconjunction with the OBSS CCA threshold value. Within the correspondingTXOP, specifically the signaling field of the second PPDU may include afield indicating that the transmission power is adjusted. Specifically,the wireless communication terminal may operate in the same manner asthe embodiments described with reference to FIG. 19 .

Although the present invention is described by using wireless LANcommunication as an example, it is not limited thereto and may beapplied to other communication systems such as cellular communication.Additionally, while the method, device, and system of the presentinvention are described in relation to specific embodiments thereof,some or all of the components or operations of the present invention maybe implemented using a computer system having a general purpose hardwarearchitecture.

The features, structures, and effects described in the above embodimentsare included in at least one embodiment of the present invention and arenot necessary limited to one embodiment. Furthermore, features,structures, and effects shown in each embodiment may be combined ormodified in other embodiments by those skilled in the art. Therefore, itshould be interpreted that contents relating to such combination andmodification are included in the range of the present invention.

While the present invention is described mainly based on the aboveembodiments but is not limited thereto, it will be understood by thoseskilled in the art that various changes and modifications are madewithout departing from the spirit and scope of the present invention.For example, each component specifically shown in the embodiments may bemodified and implemented. It should be interpreted that differencesrelating to such modifications and application are included in the scopeof the present invention defined in the appended claims.

The invention claimed is:
 1. A wireless communication terminal thatcommunicates wirelessly, the terminal comprising: a transceiver; and aprocessor, wherein the processor is configured: to receive a first PLCPProtocol Data Unit (PPDU) including a trigger frame through thetransceiver, wherein the trigger frame triggers an uplink multiuser PPDUtransmission of one or more wireless communication terminals in a firstBasic Service Set (BSS) which is overlapped with a second BSS includingthe wireless communication terminal, to receive a physical layer headerof a second PPDU which is transmitted in response to the trigger frame,wherein the physical layer header of the second PPDU comprises a spatialreuse field indicating a parameter, wherein the parameter is determinedbased on a magnitude of interference acceptable by a wirelesscommunication terminal which transmits the first PPDU when receiving thesecond PPDU, and a transmission power of the first PPDU, whenpredetermined conditions are met, to transmit a third PPDU while thesecond PPDU being transmitted and not to set a network allocation vectorbased on the trigger frame, wherein the predetermined conditions includethat a transmission power of the third PPDU is below than a value whichis determined based on a received signal strength of the first PPDU andthe parameter, and a BSS color indicated by the physical layer header ofthe second PPDU is equal to a BSS color indicated by a physical layerheader of the first PPDU, wherein the value of the parameter is a valuenormalized over a 20 MHz frequency bandwidth, and when at least one ofthe predetermined conditions is not met, to determine whether a channelthrough which the third PPDU to be transmitted is idle by using a staticClear Channel Assessment (CCA) threshold value as a reference value andtransmit the third PPDU according to whether the channel is idle whilethe second PPDU being transmitted, wherein the static CCA thresholdvalue is used for determining whether a channel is idle when thewireless communication terminal is receiving a PPDU transmitted from thesecond BSS.
 2. The wireless communication terminal of claim 1, whereinthe trigger frame comprises a field indicating the parameter.
 3. Thewireless communication terminal of claim 1, when the predeterminedconditions are met, wherein the processor is configured to determinewhether the channel through which the third PPDU to be transmitted isidle by using an overlapped BSS CCA threshold value and reduce a backoffcounter by a predetermined time period when the channel is idle, whereinthe overlapped BSS CCA threshold is for a PPDU which is transmitted froma BSS overlapped with the second BSS, wherein the backoff counter is areference value used for channel access to the channel in an existingbackoff procedure.
 4. The wireless communication terminal of claim 3,wherein the static CCA threshold is higher than the overlapped BSS CCAthreshold.
 5. An operation method of wireless communication terminalthat communicates wirelessly, the method comprising: receiving a firstPLCP Protocol Data Unit (PPDU) including a trigger frame, wherein thetrigger frame triggers an uplink multiuser PPDU transmission of one ormore wireless communication terminals in a first Basic Service Set (BSS)which is overlapped a second BSS including the wireless communicationterminal, receiving a physical layer header of a second PPDU which istransmitted in response to the trigger frame, wherein the physical layerheader of the second PPDU comprises a spatial reuse field indicating aparameter, wherein the parameter is determined based on a magnitude ofinterference acceptable by a wireless communication terminal whichtransmits the first PPDU when receiving the second PPDU, and atransmission power of the first PPDU, when predetermined conditions aremet, transmitting a third PPDU while the second PPDU being transmittedand not setting a network allocation vector based on the trigger frame,wherein the predetermined conditions include that a transmission powerof the third PPDU is below than a value which is determined based on areceived signal strength of the first PPDU and the parameter, and a BSScolor indicated by the physical layer header of the second PPDU is equalto a BSS color indicated by a physical layer header of the first PPDU,wherein the value of the parameter is a value normalized over a 20 MHzfrequency bandwidth, and when at least one of the predeterminedconditions is not met, determining whether a channel through which thethird PPDU to be transmitted is idle by using a static Clear ChannelAssessment (CCA) threshold value as a reference value and transmit thethird PPDU according to whether the channel is idle while the secondPPDU being transmitted, wherein the static CCA threshold value is usedfor determining whether a channel is idle when the wirelesscommunication terminal is receiving a PPDU transmitted from the secondBSS.
 6. The method of claim 5, wherein the trigger frame comprises afield indicating the parameter.
 7. The method of claim 5, wherein thetransmitting the third PPDU when the predetermined conditions are metcomprises determining whether the channel through which the third PPDUto be transmitted is idle by using an overlapped BSS CCA threshold valueand reducing a backoff counter by a predetermined time period when thechannel is idle, wherein the overlapped BSS CCA threshold is for a PPDUwhich is transmitted from a BSS overlapped with the second BSS, whereinthe backoff counter is a reference value used for channel access to thechannel in an existing backoff procedure.
 8. The method of claim 7,wherein the static CCA threshold is higher than the overlapped BSS CCAthreshold.